Analysis of 3D visual information processing in the parietal association cortex

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Recent neurophysiological studies have shown that the parietal cortex can be classified into sub-regions and that those regions play different roles in information processing for spatial vision. Stereopsis is the ability to perceive depth of the visual world based on images projected on the two retinae. Binocular disparities are crucial cues for building a 3D representation of the visual world, however, monocular depth cues, such as texture, shading, and linear perspective are also very important for that. Marr (Marr 1982) postulated in his theory of vision that an important step in visual information processing for 3D representation of an object is the description of the geometry of the visible surface, especially that of the surface orientation and curvature. Several kinds of disparity cues and monocular cues for the representation of surface orientation have been demonstrated from psychophysical studies. Integrative processing of these different types of depth cues is necessary to build a neural representation of the surface orientation. We examined the properties of surface orientation selective (SOS) neurons in the caudal part of the lateral bank of the intraparietal sulcus (area CIP) of alert monkeys, and identified a group of neurons which are sensitive to binocular disparity cues and also monocular depth cues. We also found that the neurons in the area CIP responded to curved surface defined by the Koenderink's formula. These neurons may contribute to the representation of the 3D feature of objects in the visual world.